The present application relates to a system and a method for determining an estimated battery state vector and an estimated battery parameter vector using digital filtering techniques.
In the context of rechargeable battery pack technologies, it is desired in some applications to be able to estimate quantities that are descriptive of the present battery pack condition, but that may not be directly measured. Some of these quantities may change rapidly, such as the pack state-of-charge (SOC), which can traverse its entire range within minutes. Others may change very slowly, such as cell capacity, which might change as little as 20% in a decade or more of regular use. The quantities that tend to change quickly comprise the “state” of the system, and the quantities that tend to change slowly comprise the time varying “parameters” of the system.
In the context of the battery systems, particularly those that need to operate for long periods of time, as aggressively as possible without harming the battery life, for example, in Hybrid Electric Vehicles (HEVs), Battery Electric Vehicles (BEVs), laptop computer batteries, portable tool battery packs, and the like, it is desired that information regarding quickly varying parameters (e.g., SOC) be used to estimate how much battery energy is presently available to do work, and so forth. Further, it may be desirable to ascertain information regarding slowly varying parameters (e.g., total capacity) in order to keep the prior calculations precise over the lifetime of the pack, extending its useful service time, and help in determining the state-of-health (SOH) of the pack.
The inventor herein has recognized that other mathematical algorithms have been unable to provide a highly accurate estimate of an internal state and a parameter of a battery because they are not sufficiently optimized for batteries having non-linear operational characteristics. Since batteries generally have non-linear operational characteristics, a more accurate method is needed.
Accordingly, the inventor herein has recognized a need for a system and a method for more accurately determining an estimated battery state and an estimated battery parameter. In particular, the inventor herein has recognized a need for utilizing two coupled “filters” with combined behavior that estimates an estimated battery state and an estimated battery parameter.